<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        #box {
            color: blue;
        }

        .box {
            color: palevioletred;
        }

        /*!important强制使用  */
        div {
            color: red !important;
        }
    </style>
</head>

<body>
    <div id="box" class="box">
        1
    </div>
</body>

</html>